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Lecture 6

ESSE 3600 Lecture Notes - Lecture 6: Vector Processor


Earth, Space Science and Engineering
Course Code
ESSE 3600

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EATS 3300 Lecture 6 Practise Questions
1. Line simplification creates a simplified line using a subset of the original vertices, while still retaining
characteristics of the original line. This process is important in spatial modeling because it helps to
reduce storage space, faster rendering, faster V2R conversion, and faster vector processing.
2. Line simplification algorithms are used to perform line simplification, and they can be categorized by
the extent of neighborliness used in the mathematical processing. The three types are local processing
algorithms, pseudo-local processing algorithms, and global processing algorithms.
3. Three basic line simplification algorithms are perpendicular distance, angular algorithms, and Lang
algorithms. In a perpendicular distance algorithm, this is local processing, and the distance from p1 to p2
is greather than the threshold distance(see slide 8). In this case, we keep p2. In a perpendicular
algorithm, also local, if the distance to p3 is less than the threshold distance, we can reject p3. In an
angular algorithm, the angle is greater than the threshold angle, and the point is kept. If the angle is less
than threshold angle, we reject p3. A Lang algorithm is pseudo-local and the user must define two
parameters, which is the number of points to look ahead, and a distance threshold parameter. If the
distance is greater than threshold, keep the point.
4. Douglas Peucker algorithms are for global processing, it considers the line in its entirety while
processing, There are two cases, if the distance is less than threshold then the straight line is deemed
suitable to represent the whole line. If the distance is greater than the threshold, then the furthest point
away becomes the new floating point. If the distance is less, then the straight line is suitable to rep the
whole line.
5. Intra-feature errors are topology errors and post processing is needed to make sure topology is right.
Inter-feature errors are topology errors where the spatial relationships between two lines are not
correct, for example one simplified line is overcrossing the other. Measures for evaluating line
simplification algorithms are line length, vector displacement, and areal displacement.
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